class Instrument():
     def make_sound(self):
         pass

class Erhu(Instrument):
    def make_sound(self):
        print('二胡在弹奏')

class Pinao(Instrument):
    def make_sound(self):
        print('钢琴在弹奏')

class Violin(Instrument):
    def make_sound(self):
        print('小提琴在弹奏')

def play(obj):
    obj.make_sound()
 
er=Erhu()
piano=Pinao()
violin=Violin()

play(er)
play(piano)
play(violin)


